A brushless motor has, for example, a stator with nine slots, a rotor with eight poles, a magnetic pole position detecting magnet with eight poles equal to those of the rotor, and three Hall ICs for detecting the rotation position of the rotor by detecting the magnetism of the magnetic pole position detecting magnet. Such a brushless motor having the rotor and the magnetic pole position detecting magnet with the same number of poles, and the three Hall ICs is referred to as a single precision brushless motor.
In comparison with the single precision brushless motor, to improve the resolution of the rotation position detection of the rotor, a brushless motor has been developed which doubles the number of poles of the magnetic pole position detecting magnet, that is, which provides the magnetic pole position detecting magnet with 2n poles for the rotor with n poles (see Patent Document 1, for example).
Such a brushless motor having the magnetic pole position detecting magnet with the number of poles double that of the rotor, and the three Hall ICs is referred to as a double precision brushless motor. According to the double precision brushless motor, it can make the resolution of the rotation position detection of the rotor twice that of the single precision brushless motor.
Patent Document 1: Japanese Patent Laid-Open No. 2002-252958.